The use of matrix addressable displays of a variety of shapes and sizes is well known. In particular, matrix addressable displays of liquid crystal display (LCD) technology are finding a wide range of application from instrumentation dials to general purpose data and video displays.
Relative to electro-mechanical displays, matrix addressable displays are simpler and more durable because they have no moving parts and they are far more versatile since the same display can be varied to depict all manner of different data. Relative to cathode ray tube (CRT) technology, matrix addressable displays are also simpler and more durable and far less bulky. In one respect, however, CRT technology is regarded as holding an advantage because it requires far fewer wires for its control. In particular, CRT's only require the control of a single electron beam regardless of the number of pixels (picture elements) which are to be displayed.
Matrix addressable displays, however, require a number of wires for their control which is at least two times the square root of the number of pixels in the display. As the number of pixels in matrix addressable displays has become large, for example, pixel numbers of two hundred and fifty thousand or more are easily realizable in current LCD technology, the connection of the control wires to a matrix addressable display has become a major engineering problem. Continuing advances in integration technology are almost certain to lead to the need to wire displays of even greater pixel counts.
It is well known that connections which can be done monolithically, on a single plane, are more reliable and simpler to manufacture. However, in the case of display devices there is often the conflicting goal of mounting the display such that any inactive border is minimized. In the case where the matrix addressable display is to be retrofitted in the form factor of older electro-mechanical or CRT displays, this problem is especially acute because these earlier displays tend to fill the surface available to them and the user generally will not accept any display whose size must be reduced to accommodate wiring requirements.
For example, in the field of aircraft instruments this connection border can account for 0.25 inch of the radius available for a conventional circular LCD display. In the older electro-mechanical displays only 0.05 inch of the available display radius was unused. Examples of the prior art for aircraft
instruments is shown in FIGS. 1a and 1b. FIG. 1a shows the actual size dial of an electro-mechanical Vertical Speed Indicator (VSI) known as a "2074 Series TCAS II." FIG. 1b shows the actual size dial of an LCD VSI known as a "2874 Series Flat Panel TCAS II."
The loss of 0.25 inch of display radius has a substantial effect on dial size as shown by the following example. If a typical aircraft gauge has a maximum display radius of 1.925 inch, then the maximum dial area (with pi=3.14) is 11.64 square inches. Current electro-mechanical technology decreases the display radius to 1.875 and decreases the dial area to 11.04 square inches. Thus 5% of the maximum display area is unused with electro-mechanical instruments. Current LCD technology decreases the display radius to 1.675 inches, decreasing dial area to 8.81 square inches. Thus 24% of the maximum display area is unused with current LCD instruments. Another way of summarizing the above data is that current LCD aircraft instruments could have dials which are 32% larger if the wiring problems could be solved.
Similar disadvantages are encountered in efforts to wire other types of matrix addressable displays or receivers.
Prior art attempts to satisfy reliability and simplicity while achieving a minimal border have been far from optimal. Typical examples are U.S. Pat. No. 4,688,896 (the '896 patent) and U.S. Pat. No. 4,836,651 (the '651 patent). In the '896 patent the row and column address lines are interdigitated (one half extending to one edge of the display and the other half to the opposite edge) so that the row and column lines can be driven from all four edges of the display. In the '651 patent the row and column lines are brought to pads on the edge of the display's mounting plane. Flex connectors are soldered to the pads and the connectors are bent perpendicularly to the plane of the display to achieve a narrow display border.
The '651 apparatus for a narrow display border is inherently unreliable and difficult to manufacture. In a typical LCD display there will be several hundred of these solder pad connections on each side of the display with a density of approximately 100 pads per inch.
This approach is inadequate when the display is subject to a great deal of mechanical stress in the environment in which it is used.